全文获取类型
收费全文 | 378篇 |
免费 | 28篇 |
国内免费 | 12篇 |
专业分类
418篇 |
出版年
2023年 | 6篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 22篇 |
2013年 | 22篇 |
2012年 | 14篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 21篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1971年 | 4篇 |
1970年 | 2篇 |
排序方式: 共有418条查询结果,搜索用时 0 毫秒
1.
Summary The developing pigment strand of rice (Oryza sativa L.) was studied by conventional electron microscopy and also by use of thick sections post-fixed with zinc iodide and osmium (ZIO).When the rice caryopsis achieves maximum length, a suberised adcrusting wall layer is laid down over the original primary walls of the pigment strand. Concomitant with suberin deposition a proliferation of tubular endoplasmic reticulum occurs in the cytoplasm giving rise to numerous interconnected vesicles which bear ribosomes. The vesicles in the general cytoplasm retain their ribosomes while those close to the wall become smooth and contain an electron-opaque granular material which is eventually deposited to the outside of the plasmalemma. This granular material may be the precursor(s) from which suberin is polymerised. The suberised wall attains about six times the width of the original primary wall and plasmodesmata, which traverse both primary wall and suberised wall layers, become greatly elongated.Lipid bodies increase in both size and frequency during development, eventually coalescing to form a complete plug across the pigment strand and occluding the symplast of this tissue. The significance of these ultrastructural observations is discussed in relation to the previously demonstrated role of the pigment strand as a translocation pathway for water and assimilates during grain filling.Abbreviations ER
endoplasmic reticulum
- ZIO
zinc iodide-osmium fixation 相似文献
2.
MICHAEL L. RACHKOVSKY 《Pigment cell & melanoma research》1991,4(3):105-111
By light microscopic investigation of skin and wool specimens of newborn lambs, we discovered a previously unknown mechanism for melanosomes transport in the process of dermal papilla melanocytes regular mitosis and migration into the hair shaft. This mechanism plays a great role in hair pigmentation especially in dominant (ED/ED) and recessive (Aa/Aa) black lambs of all investigated breeds. The rate of pigment cell mitosis, proliferation, and migration differs greatly in lambs of investigated color genotypes. In black genotypes the rate of melanocyte mitosis is very high and is approximately the same as in the hair bulb matrix cells, whereas in brown and red genotypes this rate is much lower. Melanocyte mitosis in the light red and tan groups was not found. 相似文献
3.
Z. Svab P. Maliga 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(5):637-643
Summary Callus ofNicotiana tabacum SRI, a mutant with maternally inherited streptomycin resistance, was induced from leaf sections. Callus pieces were mutagenised with N-ethyl-N-nitrosourea and inoculated onto a shoot-induction medium on which calli are normally green. White callus sectors were observed in the mutagenised cultures, and white and variegated shoots were regenerated from these sectored calli. The SR1-A10 line regenerated a chimeric shoot with white leaf margins. The chimeric shoot was grafted onto a normal green rootstock, grown into a flowering plant in the greenhouse, and crosses were made. The SRI-A15 line was crossed using flowers formed on albino plants grown in sterile culture. Pigment deficiency was maternally inherited in both lines. Physical mapping of the chloroplast genome of the SR1-A15 mutant by SalI, PstI and BamHI restriction endonucleases did not reveal any difference between the SR1-A15 and the parental SRI chloroplast genomes. 相似文献
4.
Louisa J. D. van Dijk Rinse Ubbink Luke G. Terlouw Desire van Noord Egbert G. Mik Marco J. Bruno 《Journal of biophotonics》2019,12(10)
Protoporphyrin IX‐triplet state lifetime technique (PpIX‐TSLT) is a method used to measure oxygen (PO2) in human cells. The aim of this study was to assess the technical feasibility and safety of measuring oxygen‐dependent delayed fluorescence of 5‐aminolevulinic acid (ALA)‐induced PpIX during upper gastrointestinal (GI) endoscopy. Endoscopic delayed fluorescence measurements were performed 4 hours after oral administration of ALA in healthy volunteers. The ALA dose administered was 0, 1, 5 or 20 mg/kg. Measurements were performed at three mucosal spots in the gastric antrum, duodenal bulb and descending duodenum with the catheter above the mucosa and while applying pressure to induce local ischemia and monitor mitochondrial respiration. During two endoscopies, measurements were performed both before and after intravenous administration of butylscopolamine. Delayed fluorescence measurements were successfully performed during all 10 upper GI endoscopies. ALA dose of 5 mg/kg showed adequate signal‐to‐noise ratio (SNR) values >20 without side effects. All pressure measurements showed significant prolongation of delayed fluorescence lifetime compared to measurements performed without pressure (P < .001). Measurements before and after administration of butylscopolamine did not differ significantly in the duodenal bulb and descending duodenum. Measurements of oxygen‐dependent delayed fluorescence of ALA‐induced PpIX in the GI tract during upper GI endoscopy are technically feasible and safe. 相似文献
5.
6.
南瓜果肉色素的提取及稳定性的研究 总被引:5,自引:0,他引:5
本文研究了从南瓜果肉中提取色素的方法,并对它的光、热、酸、碱稳定性进行了研究,发现其性质较稳定,且原料来源广泛,提取工艺简单,着色效果好,是食品、医药、化妆品等领域的理想添加剂。 相似文献
7.
8.
Molecular mechanisms that produce pigment patterns in the insect cuticle were studied. Larvae of the armyworm Pseudaletia separata have stripe patterns that run longitudinally along the body axis. The pattern in the cuticle became clear by being emphasized by the increasing contrast between the black and white colors of the lines after the last larval molt. We demonstrated that dopa decarboxylase (DDC) mRNA as well as protein are expressed specifically in the epidermal cells under the black stripes. The pigmentation on the stripes was clearly diminished by injection of a DDC inhibitor (m-hydroxybenzylhydrazine) to penultimate instar larvae for 1 day before molting, suggesting that DDC contributes to the production of melanin. Further, electron microscopic observation showed that the epidermal cells under the gap cuticle region (white stripe) between the black stripes contain many uric acid granules, which gives a white color. Our findings suggest that the spatially regulated expression of DDC in the epidermal cells produces the black stripes while abundant granules of uric acid in the cells generate the white stripes in the cuticle. Based on these results, we concluded that this heterogeneity in the epidermal cells forms cuticular stripe patterns in the armyworm larvae. 相似文献
9.
Markus Ernstberger Pascal Boeswetter Tobias Baselt Frank Ebert Fabiola Basan Hanno Steinke Niels Hammer Ronny Grunert Peter Hartmann 《Journal of biophotonics》2013,6(4):310-313
Thin slices of human tissues are characterized concerning reflection and transmission in a wavelength range from 400 to 1700 nm. The results are primarily useful to find a wavelength for the detection of subjacent blood vessels during surgical procedures, especially neurological surgery. The measurements have been conducted using a customized measuring station, utilizing two halogen bulb lamps and two spectrometers. This paper focuses on creating a data base with the optical properties of artery, brain, bone, nasal mucosa, and nerve. The spectral distributions are compared among each other, similarities and differences are pointed out. Each tissue has got unique spectral characteristics, whereas typical absorption bands can be found in the overall tissues, especially hemoglobin and water absorption bands. The reflectivity maxima are typically located in the red or near‐infrared. All the transmission maxima are located between 1075 nm and 1100 nm. The measurements have been conducted at the Institute of Anatomy at the University of Leipzig. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.